stripExts: don't use a cutset when removing extension

I misread what strings.Trim does, the 2nd param is a _cut set_, so this
was removing any occurance any characters in the 2nd param. Since the
file extension is always a suffix, this uses TrimSuffix.

Fixes a bug where 'virtio_blk.ko' was being trimmed to 'virtio_bl'

main_test.go

@@ -15,6 +15,7 @@ func TestStripExts(t *testing.T) {
 		{"file.tar.gz.xz.zip", "file"},
 		{"another_file", "another_file"},
 		{"a.b.c.d.e.f.g.h.i", "a"},
+		{"virtio_blk.ko", "virtio_blk"},
 	}
 	for _, table := range tables {
 		out := stripExts(table.in)